Causal Agent

Sclerotinia homeocarpa is the name that has been used for the fungus that causes dollar spot. However, recent studies have shown that the fungus most likely belongs in either the genus Lanzia or Moellerodiscus.

 

Hosts

Cultivated turfgrass species (bentgrass, bermudagrass, fescue, ryegrass, and zoysiagrass).

 

Symptoms

The overall symptom development for dollar spot varies with turfgrass species and mowing practices. On closely mowed turfgrass, such as bentgrass golf greens, the characteristic symptoms of dollar spot are small, circular, straw-colored, sunken spots that rarely exceed 2-3 inches in diameter. If the disease becomes severe, individual spots may coalesce forming larger, irregular patches of blighted turfgrass. Residential lawns and other taller turfgrasses may exhibit irregularly shaped, bleached patches of blighted grass ranging from 4-6 inches or more in diameter. Patches may coalesce to cover large areas. Individual infected leaves develop a lesion(spot) that is first pale green or yellow, then water-soaked, and finally a bleached straw color. Dollar spot lesions are characteristically bounded by a tan to reddish-brown margin. These lesions usually englarge to extend across the entire leaf. Dieback from leaf tips is also common. Individual leaf blades may have a single lesion, have many small lesions, or be entirely blighted. In the early morning when dew is present on grass blades and the pathogen is active, a white, cottony, growth of fungal strands (mycelia) may be seen on diseased turf. The mycelia disappear as the leaves dry.

 

Control

Cultural Management - Maintain moderate to high nitrogen fertility during periods favorable for dollar spot development. For warm-season turfgrasses (bermuda and zoysia), a total of five pounds actual nitrogen (N) per 1000 square feet should be applied as five one-pound N per 1000 square feet split applications in May, June, July, August, and September. Do not apply N after September 15, as this increases turfgrass susceptibility to winter injury and spring dead spot disease development. For cool-season turfgrasses (bent, blue, fescue, and rye), four pounds N per 1000 sq feet per year should be applied as one pound N per 1000 sq feet applications in March, May, September, and November. When water is required, apply a sufficient amount for deep penetration, and then water as infrequently as possible without causing moisture stress between waterings. Avoid frequent applications of small amounts of water. Do not water in the late afternoon or evening, for this prolongs periods of leaf wetness at night. Promote good air circulation over the turf by pruning or removing trees or shrubs and removing other barriers to air movement. Mow the turfgrass regularly at recommended heights. Chemical Management - If nitrogen fertility levels are properly managed, the use of fungicides for dollar spot control in residential lawns is normally not necessary. However, many effective fungicides are available for dollar spot management if needed. Chemical control is most effective if different fungicides are alternated and applied in the early spring and fall before disease development, or when the disease is first evident. Fungicides should be used in conjunction with good turfgrass cultural management practices. Please contact your local county extension office for current information.